The following tutorial will show you around the part 479 landing page.
27 CFR Part 447
Importation of Arms, Ammunition and Implements of War
27 CFR Part 478
Commerce in Firearms and Ammunition
27 CFR Part 479
Machine Guns, Destructive Devices, and Certain Other Firearms
27 CFR Part 555
Commerce in Explosives
27 CFR Part 646
Contraband Cigarettes
27 CFR Part 771
Rules of Practice in Explosive License and Permit Proceedings
Effective date is the date this part was last amended
A firearm may be transferred to the United States or any department, independent establishment or agency thereof without payment of the transfer tax. However, the procedures for the transfer of a firearm as provided in § 479.90 shall be followed in a tax-exempt transfer of a firearm under this section, unless the transferor is relieved of such requirement under other provisions of this part.